Take a familiar (or at least famous) quote (e.g. "Don't go around saying the world owes you a living. The world owes you nothing. It was here first." by Mark Twain). Then find a good stopping point (e.g. "Don't go around saying"). After this, add the phrase, "I'm not wearing any pants (e.g. ""Don't go around saying, "I'm not wearing any pants!").
Stevie - Colour Sergeant Bourne! Take three sections and form a flying platoon! And for God's sake put on your pants!
Stevie - You think you lost your love
Well I saw her in Northants
It's you she's thinking of
Not wearing any pants
Stevie - Let the wind blow high
Let the wind blow low
Through the street in a kilt I'll go
All the lassies say 'Hullo!'
'Donald where's your troo
haaaaaang on a minute.
Stevie - Double, double, toil and trouble
Fire burn and cauldron bubble
Eyes of newts and legs of ants
Macbeth's not wearing any pants
W Churchill -
We shall fight on the beaches, we shall fight on the landing grounds, we shall fight in the fields and in the streets, we shall fight in the hills, even when we're not wearing any pants.
blamelewis - I have in my hand a pair of pants... (Striving for accuracy in the pursuit of the trivial I find from my meagre researches that Chamberlain's famous quote seemingly isn't in fact a quote. However as Humph used it on Clue I reckon it's ok...)
Geo - ...and now class: to demonstrate Newton's Third Law, I am not wearing any pants.
Stevie - I know what you're thinking, punk. You're thinking "did he fire six shots or only five?" Now to tell you the truth I forgot myself in all this excitement. But being this is a .44 Magnum, the most powerful handgun in the world and will blow your head clean off, you've gotta ask yourself a question: "Why ain't that cop wearing any pants?"
Pooh -
In Dixie Land where I was born in,
Early on one frosty mornin,
Look away! Look away! Look away! Sheesh! I ain't wearin' no pants.
Stevie - Salt? Vinegar? Pants?
Phil - No sun - no moon!
No morn - no noon -
No dawn - no dusk - no proper time of day.
No warmth, no cheerfulness, no healthful ease,
No comfortable feel in any member -
No shade, no shine, no butterflies, no bees,
No fruits, no flowers, no leaves, no birds! -
No pants!
Geo - The year’s at the spring,
And day’s at the morn;
Morning’s at seven;
The hill-side’s dew-pearled;
The lark’s on the wing;
The snail’s on the thorn;
God’s in His heaven—
And I'm not wearing any pants!
Pablo - To be sung (with great heartiness) to the tune of Beethoven's Ode to Joy:

When I stride out on the highway
Much attention's paid to me,
Anything from sideways looks
To groans of female ecstasy.

Giggles, blushes, winks and nudges,
Many an admiring glance,
For I am a well-built bugger
And I don't wear any pants.
Raak - "Toto, I don't think we're wearing pants any more."
blamelewis - (Scarecrow):
I could while away the hours
Conferrin' with the flowers
Consultin' with the ants
And my groin I'd be scratchin'
While my thoughts were busy hatchin'
If I only had some pants
Stevie -
Love is a stranger in an open car
Tooling around not wearing any pants
Boolbar -
Winter is coming ... and I'm not wearing any pants!
Kim -
I hope you don't mind
I hope you don't mind
That I'm not wearing any pants
Boolbar - Captain's Log, Stardate 427089.4   Our mission to boldly go where no man has gone before has entered a new phase. The entire crew are not wearing any pants.
Geo - "...what woman has ever stopped by a want of information? She felt. And despised him for not wearing any pants." -[John le Carr¨] Tinker, Tailor, Soldier, Spy.
S Coleridge -
"Water, water everywhere...
and yet no pants to wear"
Geo - ...and so I replied to St. Peter at the gate: "Not bloody likely. I'm not wearing any knickers."
Stevie - "I will not be pushed, filed, stamped, indexed, briefed, debriefed or numbered. Actually, as you were on the debriefed bit. It appears I am not wearing any pants."
Stevie - Oh say, have you heard the fate
Of Mr PP Bliss and Wife
Of their deaths I shall relate
Also Others lost their life
They were not wearing any pants
In the Ashtabula Bridge disaster where so may died
And their bodies were infested with ants
Once the river receded and the mud had dried.
William Topaz McGonagall -
Oooooooooooooooooooooooo
Twas in the year eighteen eighty-two
That a great dance took place in Scotland the noo
It was held in the magnificent city of Aberdeen
Where many gaily-dressed couples were to be seen.
And among these couples were some from the fair nation of France
Who on spying the Scotsmen in kilts were amazed that they could dance without any pants.
Brother TROLL -

The moat is deep
The fortress tall
A sentry patrols
Atop its stout wall

The gate is secure
Ivy clings in its sleep
The Queen's in her chamber
The King's in his Keep

The bard he/she writes
The dreamer he/she dreams
Unaware that a TROLL is in the storeroom
Not wearing any pants
Stevie - Lo there do I see my father,
Lo there do I see my mother,
my sisters and my brothers,
Lo there do I see the line of my people,
back to the beginning.
Lo, they do call me,
they bid me take my place among them,
in the halls of Valhalla,
where the brave are not wearing their pants.
Stevie - And who can forget that scene from the 70s movie The Shining in which Shelly Duvall picks up Jack Nicholson's novel-in-progress and reads:

I'm not wearing any pants
I'm not wearing any pants
I'm not wearing any pants
I'm not wearing any pants
I'm not wearing any pants
I'm not wearing any pants
I'm not wearing any pants
I'm not wearing any pants
I'm not wearing any pants
I'm not wearing any pants
I'm not wearing any pants
I'm not wearing any pants
I'm not wearing any pants
I'm not wearing any pants
I'm not wearing any pants

Kim - [Steve] Re: the pantless Prisoner - I chuckled.
Kim - So off went the Emperor in procession under his splendid canopy. Everyone in the streets and the windows said, "Oh, how fine are the Emperor's new pants! Don't they fit him to perfection? Nobody would confess that they could "see everything" for that would prove him either unfit for his position, or a fool. No costume the Emperor had worn before was ever such a complete success.

"But he's not wearing any pants!" a little child said.

And we all know what happened then, don't we, children?

penelope - 'I know it's only rock and roll, but I'm pantless, pantless, yes I am': Mick Jagger & the Rolling Stones.
Stevie - Oh he sits at the corner of Beggar's Bush
And the crowd looks on in a trance
As the dolls at the end of the plank do a dance
And he croons "I'm not wearin' me pants"
La-la-la-la
Come day, go day
Wish in me heart it was Sunday ... etc etc
Plump - Michael Caine : You are only supposed to blow the bleedin drawers off cos he ain't wearing any pants
Stevie - The Thief Baggins: What have I got in my pocket?

Gollum: Not fair, my precious! It hasn't got any pocketses! It isn't wearing any pants!

A Conan Doyle - "Elementary my dear Watson. I knew this man was about to burgle the offices of the Sunnydale Nudist Colony because he wasn't wearing any pants"
Guido - "Laban's technique is based on the theory that all movement is a reaction to gravity. If we ask the dancer to allow gravity to take over body parts in a normal stance you will notice that her spine becomes more curved, her head drops, her knees may bend slightly, her shoulders will round and her arms will fall in front of her body. If we wanted to attach emotional qualities to this, or in other words, try to read her body language, we might use words like...I'm not wearing any pants."
Kim - After nearly a month building up sufficient LV, I have finally arrived at Mornington Crescent and I am most definitely not wearing any pants!. If only dear Mrs Trellis could see me now......
Audience
*shouts, screams, generally goes wild for Kim*
Stevie - Silent night, Holy night
All is calm, All is bright
Round yon virgin not wearing her pants
sound of needle being dragged across record
Stevie - Weeeeeeeeeee
wish you a merry Christmas
We wish you a merry Christmas
We wish you a merry Christmas
Not wearing our pants.
Stevie - And my absolute favorite bop-along carol (bass part in italics):

Joy to the world! the Lord is come;
Let earth receive her King;
Let every heart prepare him room,
Not wearing any pants
              Not wearing any
Not wearing any pants
paaaaaaants, Not wearing any
Not wearing, not wear-air-airing any pants
paaaaaaants, not wear-air-airing pants, pants, pants

Falstaff - "Yes, I agree, there does appear to be a draft in here. I'll go and put on my pants!!!"
This is the end of the line. There is no more.